This proposal describes a 4-year training program for the development of my academic career in Pediatric Infectious Diseases. I have completed formal residency in General Pediatrics and subspecialty fellowship training in Pediatric Infectious Diseases at the Children's Hospital of Philadelphia (CHOP), and am now expanding my scientific skills in NKT cell biology and tumor immunology, and developing my clinical skills in the infectious diseases of immunocompetent and immunocompromised hosts. Drs. Kim Nichols and Gary Koretzky will be mentoring my scientific development. Dr. Nichols, the Director of the Hereditary Cancer Disposition Program at CHOP, and Associate Professor of Pediatrics at the University of Pennsylvania (Penn), is an expert in NKT cell biology. Dr. Nichols has a growing track record of developing the careers of fellows, post-doctoral trainees, and junior faculty. To make my mentoring team as strong as possible, Dr. Nichols has partnered with Dr. Koretzky, Vice-Chair of Research and Chief Scientific Officer in the Department of Medicine at Penn, and the Director of the Signal Transduction Program in the Abramson Family Cancer Research Institute. Dr. Koretzky is an international authority on lymphocyte biology and T cell signal transduction with extensive experience in successfully mentoring numerous students, post-doctoral fellows, and junior faculty members. To further promote my scientific development, I have composed a Scientific Advisory Committee of highly-regarded physician-scientists consisting of Drs. Jordan Orange, Stephan Grupp, and Jeffrey Bergelson. Additionally, Dr. Paul Offit, Maurice Hilleman Endowed Chair in Vaccinology, Professor of Pediatrics at Penn, and Chair of Infectious Diseases at CHOP, will help guide me regarding my clinical development. The proposed research focuses on the tumor immunosurveillance mediated by invariant natural killer T (iNKT) cells. iNKT cells are innate lymphocytes that play critical roles in host immunity, including protection from specific pathogens and tumors. These cells are known to participate in anti-tumor responses indirectly via the robust production of cytokines that promote the anti-tumor activity of natural killer (NK) and CD8+ T cells. In studies using the iNKT cell hybridoma line, DN3A4-1.2, and primary murine and human iNKT cells, I find that iNKT cells themselves exhibit direct cytotoxicity in vitro against CD1d-positive tumors when the target cells are loaded with stimulatory glycolipid antigens. Additionally, in the absence of perforin, this in vitro iNKT cytotoxicity is greatly reduced. Finally, in an in vivo model in which the direct tumor surveillanc capacity of iNKT cells can be evaluated in the absence of other lymphocytes, I find that murine iNKT cells are sufficient for clearance of CD1d-expressing glycolipid-loaded tumors. Based on these observations, I propose to further dissect the mechanisms governing iNKT cell-mediated immunosurveillance. Specifically, I will define the optimal requirements for control of tumor growth in vivo by murine and human iNKT cells and the importance of stimulatory glycolipid antigens in this process (AIM 1). In AIM 2, I will examine the expression and cellular localization of cytolytic effector molecules in resting and activated murine and human iNKT cells, and then evaluate the requirement of these molecules for in vivo tumor immunosurveillance. Finally, in AIM 3, I will examine whether the stimulatory cytokine interleukin-2 augments iNKT cell cytotoxicity in vitro and in vivo and I will explore the mechanisms underlying the augmentation of iNKT cell killing capacity. The completion of the proposed studies will help define the direct axis of iNKT cell cytotoxicity and tumor immunosurveillance in vivo, and should provide insights into the future use of these cells in the adoptive cellular therapy of cancer. Collectively, CHOP and Penn provide an ideal scientific environment for my training as a physician-scientist. I will take advantage of the intellectual strength and academic track-record of my co- mentors and scientific advisory committee members, and the robust availability of expertise, facilities, and resources afforded at CHOP and Penn to accomplish this proposed training program.